WASHINGTON — It took months of “quiet diplomacy,” a change in U.S. presidents and an American diplomat’s extraordinary, secret visit to Pyongyang to bring Otto Warmbier home.

U.S. special envoy Joseph Yun was a household name to almost no one before Warmbier’s return to Ohio on Tuesday, yet he joins an exceedingly short list of U.S. officials to set foot in furtive North Korea in recent years. The last such visit is believed to have been in November 2014, when former National Intelligence Director James Clapper brought home two other jailed Americans.

New details that emerged Thursday about Yun’s brief visit to the North Korean capital illustrate the deep level of estrangement between the U.S. and North Korea, two countries that don’t have diplomatic relations and have technically been in a state of war for more than half a century, despite the armistice that ended the Korean War.

When Yun finally laid eyes on the comatose Warmbier in a North Korean hospital, it was the first time the U.S. could verify his condition in person since his sentencing more than a year earlier, the State Department said.

For Yun, a longtime Asia hand who joined the foreign service in 1985, the trip was the culmination of a series of delicate and rare conversations between the U.S. and North Korean officials that transpired since President Donald Trump took office.

They started in Norway, playing the role of neutral third party, and moved to New York, where North Korean diplomats are accredited at the United Nations.

Warmbier, 22, spent almost a year-and-a-half in captivity after being arrested in January 2016. The North accused the University of Virginia student of entering the country under the guise of a tourist and plotting against the nation’s unity with “the tacit connivance of the U.S. government.”

Paraded before the media a month later in Pyongyang, he tearfully apologized for attempting to steal a political banner from a staff-only section of his hotel. The Swedes, who represent U.S. interests in North Korea, managed to visit him in March 2016, a few weeks before he was sentenced to 15 years hard labor.

What happened next, and how Warmbier ended up in a coma, is still unclear.